This study examines the prevalence of anorexia nervosa and bulimia nervosa in relatives of probands, and examines the probandwise specificity of any familial clustering.

Data were collected from probands using the family history method.

Probands were recruited in a sequential cohort fashion.

Information collected from probands was rated semiblindly by two of the authors, and a diagnostic hierarchy applied to arrive at a diagnosis for each of the relatives assessed.

Data are reported on 2,125 family members, collected from 93 probands.

Diagnostic agreement between raters was high, with serious disagreement present in three of 167 possible cases of an eating disorder.

Rates of anorexia nervosa, bulimia nervosa, major depression, and substance abuse declined from first-to third-degree relatives, which is consistent with genetic clustering, and there was evidence of a cohort effect operating for anorexia nervosa and bulimia nervosa.

The rates of anorexia nervosa and bulimia nervosa in all family members were 5.1%, and 4.3% respectively.

An analysis of maternal and paternal descent showed no evidence for X-linked dominant transmission in these families.

Preliminary analysis of the clustering of diagnoses in relatives showed a tendency (X2=14.47, P=006) for family members to be affected by the same diagnosis as was the proband. (...)